Change of management query

Hi everyone, I wonder if anyone can help me… our present LL inherited our property, and as they live overseas, have now employed a letting agency.
The agency told us of this, and urged us - are still harassing us actually - to get everything they want done immediately. They only gave us ten days notice for a rent increase… They are trying to get us to commit asap because for two years the LLs have not fulfilled any of their legal obligations, so they cannot get an S21. (The plan was to sell, then a change of mind for a year).
My questions are:

  1. Are we legally obliged to sign the new AST agreement, or can we decline and stay on a rolling tenancy, seeing as it’s now effectively a new LL?
  2. Where do we stand with regards to them asking for a rent increase without sufficient notice - how can we trust a company which does that?
  1. You dont need to sign a new ast. The new landlord takes over the responsibilities under existing tenancy so you can just leave it on rolling basis.
  2. You can confirm to them that increase isnt valid and you require the 1 months notice.

Have they given a formal Section 13 notice for rent increase?